1. The Field of the Invention
The present invention pertains to polyolefin staple fibers treated to render them suitable for fluidizing and conveying by air ("airveying") without the generation of static charge and which are sufficiently oleophilic to be useful for reinforcing pavement. The invention also relates to the use of such staple fibers in pavement and geoways, and to methods for making pavement and geoways using the staple fibers.
2. The State of the Art
In the paving and repairing of synthetic load-bearing vehicular geoways, such as roadways, aircraft and aeronautic takeoff/landing runways and launch pads, and similar surfaces, an asphalt cement (i.e., pure asphalt) is typically used as a base material. Asphalt cement is comprised of asphalt and/or bitumen combined with flux oil (i.e., oil obtained from asphalt-base petroleum, typically 20.degree.-25.degree. Be). The asphalt cement is typically mixed with coarse graded mineral aggregate, such as broken stone, slag, or gravel mixed with sand, to produce an asphalt concrete used as the commonly recognized roadway surface. Asphalt-type cement compositions typically contain asphalt cement, rubber, or mixtures of asphalt cement with rubber and/or acrylic copolymers, and asphalt-type concrete compositions contain an asphalt-type cement and aggregate materials. The superambient softening temperature of the asphalt cement in the asphalt concrete requires that the concrete be processed to an elevated temperature to allow its flowable application to the surface being paved or repaired.
Polymeric fibers have been used, among other applications, for the reinforcement of engineering compositions having a variety of utilities. Asphalt-type pavements frequently contain synthetic polymeric staple fibers to improve flexibility and durability of the pavement. For instance, Duszak et al., in U.S. Pat. No. 4,492,781 (the disclosure of which is incorporated herein by reference), describe a fiber-reinforced asphalt-type pavement comprising an emulsifying agent, a water-soluble polymer, and 0.25% to 10% of reinforcing fibers, such as polyethylene or polypropylene staple fiber about 0.1 to 20 mm long, as well as conventional aggregate and thickening and curing agents, for application to surfaces as a hot mixture or as an emulsion. Either hot mix or emulsified asphalt-type compositions may be applied as a filler for underlying cracks in the surface as a waterproof layer between old and new pavements, or as an external surfacing material. These different uses as filler and as new pavement involve differences in the amount and fineness of aggregate, the concentration and length of the reinforcing fibers, and the use of different and various conventional additives.
Synthetic staple fibers such as polypropylene and polyethylene fibers are desirable because they are compatible with asphalt-type pavements. The longer lengths and higher concentrations of reinforcing fibers that facilitate interconnections between the fiber and the asphalt matrix, and an increase in durability, nevertheless adversely effect the pumpability (flowability) of the pavement and tend to produce clumping of the fibers. The addition of reinforcing fibers also requires a higher processing temperature range than the conventional 140.degree.-150.degree. C. (284.degree.14 302.degree. F.) range for convenient hot application.
Fry, in U.S. Pat. No. 4,422,878 (the disclosure of which is incorporated herein by reference), describes asphalt-type pavements containing about 4-10 wt. % of a fibrous filler, about 2.5 to 15 wt. % of a mixture of eighteen-carbon fatty acids, and up to about 30 wt. % rosin.
Leibee et al., in U.S. Pat. No. 4,662,759, and Trimble, in U.S. Pat. No. 4,502,814 (the disclosures of which are incorporated herein by reference), respectively disclose devices useful for admixing reinforcing fibers into an asphalt-type pavement and for the continuous deposition of a fiber- and asphalt-containing pavement.
Modrak, in European Patent Appln. No. 494,326 (the disclosure of which is incorporated herein by reference), describes fiber-reinforced asphalt pavements characterized in that the reinforcing fibers are bicomponent fibers comprising a polyolefin-containing bonding component conjugated with a polyolefin-wettable reinforcing component.
As part of the conventional processing of many fibers, an antistatic composition is typically applied to the fiber after spinning. After the fiber is spun it is routed at high speed to various physical and chemical treatments by the use of guides, rollers, and other conveying hardware. To ameliorate friction between the fiber and the conveying hardware, the art typically applies a lubricating finish to the fiber after spinning (a spin finish). Even with use of a lubricant, contact between the moving fiber and the stationary hardware can generate static electricity. Accordingly, the art may also apply an antistatic composition to the fiber. Antistatic compositions typically function by at least one of three methods: improving the surface conductivity to allow the electrons to move to ground or the atmosphere; attracting molecules of water to the surface, again improving the surface conductivity; and developing an electric charge opposite that of the fiber, which neutralizes the electrostatic charges.
Examples of fibers having an antistatic composition are described by Schmalz in U.S. Pat. No. 4,938,832 and EP 0 486 158 A2 (corresponding to U.S. patent application Ser. No. 914,213, filed Jul. 15, 1992) (the disclosures of which are all incorporated herein by reference), in which the spun fiber is treated with a blend of compositions comprising at least one amine or alkali metal neutralized phosphoric acid alkyl ester (an antistatic component) and a siloxane lubricant.
Harrington, in EP 0 557 024 A1 (the disclosure of which is incorporated herein by reference), describes a polyolefin fiber having an antistatic finish comprising at least one neutralized C.sub.3 -C.sub.12 alkyl or alkenyl phosphate alkali metal or alkali earth metal salt and a solubilizer, or a neutralized phosphoric ester salt having the general formula (MO).sub.x --(PO)--(O(R.sub.1).sub.n R).sub.y wherein generally M is an alkali or alkali earth metal, R.sub.1 is a short chain alkylene oxide, R is a long chain alkyl or alkenyl group, and x and y are natural numbers having the sum of 3. The solubilizer can be selected from among glycols, polyglycols, glycol ethers, and the aforementioned neutralized phosphoric ester salts.
Johnson and Theyson, in U.S. patent application Ser. No. 08/115,374, filed Sep. 2nd, 1993, now U.S. Pat. No. 5,403,426 and in European Patent Appln. No. 0 516 412 (the disclosures of which are incorporated herein by reference), describe a finish comprising a polyol or a derivative thereof formed by reacting the polyol with a fatty acid or a short chain alkylene oxide, and an antistatic finish comprising an amine or alkali metal neutralized phosphoric acid ester of the general formula (MO).sub.x --(PO)--(OR).sub.y wherein M is an amine or alkali metal, R is an alkyl group, and x and y are natural numbers having the sum of 3. The fibers may also have an overfinish comprising a polysiloxane (lubricant) and the antistatic finish just mentioned.
One drawback to using an antistatic finish on a fiber used for reinforcing pavement is that the use of relatively high amount of such finishes renders the fiber less oleophilic, and thus less compatible with the asphalt cement (and similar materials) in the pavement.